The present invention relates to a method of false twist texturing a synthetic yarn to a crimped yarn, as well as the resulting crimped yarn.
It is known to texture flat synthetic yarns for purposes of improvement. In this process, the strands of synthetic filaments, which form the yarn, are crimped, so that the yarn has a more textilelike appearance, and thus receives the therewith connected characteristics. To produce the crimp, false twist texturing has shown to be especially useful due to the high productivity at high yarn speeds. In this production, a false twist unit imparts to the yarn a false twist, which is set within a false twist zone by heating and cooling. After passing through the false twist unit, the yarn is again untwisted, with the individual filaments exhibiting a crimp. A thus-produced crimped yarn distinguishes itself by a very uniform cohesion of the individual crimped filaments, which leads to a very uniform, more or less bulked yarn cross section. To produce such crimped yarns, it is necessary that the yarn speed and the false twist produced by a false twist unit be in a certain ratio. In the case of a disk friction false twist unit, the twist imparted by the friction disks is determined by the circumferential speed D of the disks. Thus, the yarn twist is determined by the ratio of circumferential disk speed D/yarn speed Y. As is known, for example, from DE 195 26 905, the speed ratio is maximally at D/Y=2.2 at yarns speeds up to about 1,000 m/min. In this range, a saturation of the twist impartation sets in, since an increase in the twist impartation is no longer realizable. Only for purposes of realizing higher yarn speeds of more than 1,000 m/min., does DE 195 26 905 propose to increase the speed ratio D/Y to obtain an adequate crimp of the filaments.
In the crimped yarns produced by false twist texturing, the individual filaments extend side by side in the form of a strand, but intertwine relatively very little, so that there develops only a relatively low yarn cohesion of the filament bundle.
It is therefore an object of the invention to further develop the initially described method of false twist texturing such that it is possible to produce a crimped yarn with a high yarn cohesion between the individual filaments.
A further object of the invention is to create a crimped yarn, which comes as close as possible to the character of natural fibers as regards its bulkiness, hand, and appearance.
The above and other objects and advantages of the present invention are achieved by the provision of a false twist texturing method wherein the yarn is advanced into a false twist zone at an advancing speed w1, heated within the false twist zone, and cooled within the zone. False twist is produced which is above the saturation limit, preferably above about 2.2 times the yarn speed. The yarn is withdrawn so as to draw the yarn in the false twist zone not greater than 1.4 times the advancing speed w1 and less than 1000 m/min. The yarn is then wound into a package.
The resulting crimped yarn is composed of synthetic filaments which are intertwined irregularly in such a manner that large yarn cross sections (d1, d3) and small yarn cross sections (d2) alternate with each other. The cross sections are composed of curls and bows, with the curls and bows of yarn cross sections (d1, d2) being twisted in opposite directions.
Contrary to the prevailing opinion that in false twist texturing, the speed ratio of the false twist unit speed D to the yarn speed Y should not exceed a certain value at a predetermined yarn speed, the method of the present invention deliberately produces an excessive twist in the yarn. Thus, the imparted twist is above the saturation limit. From this follows that after passing through the false twist unit, the yarn continues to have a residual portion of twist. A stable yarn path is ensured by heating the yarn within the false twist zone to a temperature of more than 200xc2x0 C. and by limiting the withdrawal speed and, thus, restricting the draw ratio to 1.4 times the advancing speed. For false twist texturing by the method of the present invention, the yarn first advances at a speed w1 into a false twist zone. At the end of the false twist zone, a false twist unit imparts to the yarn a false twist, which is at a speed ratio formed between a speed D of the false twist unit and a yarn speed Y with D/Y above a saturation limit of 2.2. Within the false twist zone, the yarn is heated in a heating device to a temperature above about 200xc2x0 C., preferably in the range from 230xc2x0 C. to 270xc2x0 C., and subsequently again cooled by a cooling device downstream thereof. A second feed system withdraws the yarn from the false twist zone at a speed w2. To draw the yarn in the false twist zone, the withdrawal speed is adjusted at most to 1.4 times the advancing speed w1. In this instance, the withdrawal speed w2 is less than 1,000 m/min., so that the yarn undergoes excessive twisting. Subsequently, the yarn is wound to a package.
The thus-produced crimped yarn distinguishes itself by a high yarn cohesion with an irregular structure, which comes very close to the characteristics and appearance of natural fibers. The filaments forming the crimped yarn exhibit deformations in the form of curls, loops, and bows, which are otherwise known only in the case of yarns that were produced by the air texturing method. The synthetic filaments irregularly intertwine in such a manner that large and small yarn cross sections alternate with one another. In this connection, the curls and bows of adjacent, different yarn cross sections extend relative one another with opposite directions of twist. Thus, the crimped yarn as a whole shows no twisting tendency. In their frequency and elongation, the different yarn cross sections with opposite directions of twist are dependent on the degree of excessive twisting.
To make the changes of the cross section in the crimped yarn reproducible, a variant of the method has proved to be especially useful, wherein the false twist is imparted to the yarn by a false twist unit comprising a plurality of friction disks. The speed D of the false twist unit is determined by the circumferential speed of the friction disks. Preferably, the circumferential speed of the friction disks ranges from 2.5 times to 3.2 times the yarn speed Y, which is thus clearly above the saturation and leads to an excessive twisting of the yarn in the false twist zone.
To realize in the false twist texturing process very high speed ratios, a variant of the method shown to be especially useful, wherein the yarn undergoes only little drawing in the false twist zone. In this instance, the withdrawal speed w2 is in the range above 1.05 times the advancing speed w1.
In a further development of the method, the yarn advances for purposes of obtaining in the crimped yarn open curls, loops, and bows, through an entanglement nozzle, before it enters the false twist zone. This increases the intensity of the curl formation. In this instance, the entanglement nozzle may be used both for advancing and entangling the filaments or only for entangling the filaments. In particular in the latter case, the yarn advances to the entanglement nozzle at a speed w1.1, which is greater than the advancing speed w1. With that, the yarn is overfed into the entanglement nozzle, which enables the filaments to entangle among one another.
In a further advantageous variant of the method, the yarn withdrawn from a feed yarn package undergoes a first partial drawing in a draw zone, to then advance for entangling or for draw texturing directly into the false twist zone. This variant of the method is especially suitable for POY feed yarns, in order to be able to advance the yarn safely in the false twist zone.
To produce a not highly elastic crimped yarn, the further development of the method is proposed wherein the yarn undergoes an aftertreatment by heating after receiving the false twist and before being wound to the package.
The method of the present invention makes it possible to produce a crimped yarn, which comprises characteristics that otherwise are known only from air textured yarns. To increase the natural character of the crimped yarn according to the invention, the changes of the yarn cross section in sequence and size are made irregular. In this instance, individual yarn cross section may extend over a yarn length in the range from 0.5 mm to 10 mm.
To produce the crimped yarn of the present invention, an apparatus has turned out to be especially useful which includes a first feed system, a heating device, a cooling device, a false twist unit, a second feed system, and a take-up device. In accordance with the invention, an entanglement nozzle for advancing and/or entangling the yarn is arranged upstream of the first feed system. With that, the characteristic curl formation of the false twist textured crimped yarn is especially intensified.
To realize an adequate interlocking engagement of the filament bundles already during the entanglement, a delivery system may be associated to the entanglement nozzle. This delivery system can be operated at a speed w1.1, which is greater than the advancing speed w1 of the first feed system.
Advantageous further developments of the invention are described below.